The present invention relates to an oil application roller for applying release oil to a fixing roller of a fixing device for use in monochrome printers, color printers, copying machines, facsimile machines, etc. The present invention also relates to a seal ring for use in the oil application roller and a fixing device using the oil application roller.
Color toner for use in image forming apparatuses, such as copying machines, printers, and the like, for forming full-color images through an electrophotographic image forming process needs to have an excellent light transmittance when fixed on recording materials. Accordingly, heretofore, color toner based on a binder resin, which can melt quickly and has a low melt viscosity, has been used, and a method of fixing this color toner by a fixing device equipped with a silicone-rubber based heating roller as a fixing roller has been employed.
However, since the above-mentioned fixing device employs the fixing roller whose surface is formed of silicone rubber and the color toner based on a binder resin, which can melt quickly and has a low melt viscosity, xe2x80x9chot offsetxe2x80x9d, a phenomenon in which melted color toner adheres to the surface of the fixing roller, is liable to occur. Therefore, to prevent the hot offset, a considerable amount of a release agent, e.g., silicone oil having a great affinity for silicone rubber and being relatively inexpensive, is applied to the surface of the fixing roller.
Also, in recent years, a release component is added to the toner itself to prevent the hot offset. In this case, however, application of the release agent is still necessary, although the amount of the release agent may be small.
Conventionally, oil application rollers in various roll shapes have been proposed as a member for applying oil to the members involved in a fixing operation or the like. One example is the oil application roller disclosed in JP 1(1989)-60144B. The oil application roller includes a pipe with a number of pores on its outer periphery, release oil held in the central portion of the pipe, and heat-resistant felt made of Nomex or the like wound around the outer periphery of the pipe. JP 61(1986)-104469U discloses an oil application roller in which heat-resistant felt is wound around a member covered with a porous material such as paper to control the amount of oil exuding from the felt and to diffuse the oil in the axial direction of the oil application roller so as to attain the uniform application of the oil throughout a fixing roller. JP 5(1993)-123623A discloses an oil application roller in which silicone rubber sponge or the like is provided as an intermediate layer so as to impart elasticity to the oil application roller. Further, JP 61(1986)-104469U discloses an oil application roller in which a heat-resistant porous material other than heat-resistant felt is used.
However, in these conventional oil application rollers, controlling the amount of oil applied to the fixing roller is difficult since the oil exuding from the felt or porous material provided on the surface of the oil application roller is applied directly to the fixing roller to migrate thereto. On this account, as an oil application roller capable of controlling the amount of oil applied to the fixing roller, there has been proposed an oil application roller in which a heat-resistant microporous film layer (oil permeation control layer) is provided on the surface of felt or a porous material, thereby controlling the amount of oil passing through the layer (JP 61(1986)-183679A). Further, as an oil application roller capable of applying a smaller amount of oil uniformly and with high accuracy, there has been proposed an oil application roller in which, in place of the microporous film, a composite film obtained by filling the pores in a microporous film with a mixture of silicone rubber and oil is used as an oil permeation control layer (JP 62(1987)-178992A).
However, in these conventional oil application rollers, the amount of oil supplied to the oil permeation control layer needs to be kept constant so that the oil permeation control layer can control the amount of oil passing therethrough stably. In addition, in order to attain a stable oil application over a long time period, these oil application rollers desirably include an oil holder with a two-layer structure including an oil supply layer and an oil diffusion layer.
In this case, a difference in osmotic pressure is required between the two layers so that oil can move. In addition, the porosity (the ratio of the volume of pores to the total volume) of the oil supply layer is required to be higher than that of the oil diffusion layer. Also, for an extended service life of the oil application rollers, the porosity of the oil supply layer is required to be high. However, an increase in the porosity of the oil supply layer results in a decrease in its oil holding power, thereby causing a problem that an oil leak is liable to occur. Moreover, if an oil tank is used instead of the oil supply layer, the risk of the oil leak further increases.
Furthermore, when release oil comes into contact with the microporous film or composite film used as an oil permeation control layer, the pores in the microporous film are closed by the release oil. As a result, if large volumes of gas are generated abruptly, smooth permeation of the gas becomes difficult. If the gas is forced to pass through the pores, a pressure of several millions of Pa is required, for example. For this reason, if the pore diameter of the microporous film is made smaller to decrease the amount of oil passing through the film, the higher pressure is required. Moreover, when the composite film as described above is used as an oil permeation control layer, it is difficult to allow the gas to pass though the film without breaking the film.
Furthermore, vapor pressure is created by the moisture absorbed in the oil and the porous material at the time of heating and cooling the members involved in a fixing operation. In addition, pressure also is created by the thermal expansion of air in the oil application roller. As a result, the oil permeation control layer is subjected to an excessive pressure. This may cause the oil to spout out, thereby increasing the amount of the oil applied initially. Further, in some cases, the oil permeation control layer may be broken or swollen like a balloon.
In order to prevent the above troubles, providing a vent hole, which allows the pressure inside the oil application roller to be released, in a seal ring provided at each end face of the oil application roller has been proposed (JP 11(1999)-219059A).
However, the conventional oil application roller provided with a vent hole suffers the following problem. If the user detaches the oil application roller from the fixing device and leaves the roller in the state where the rotation axis thereof runs vertically during use, the oil will be unevenly distributed in the roller due to gravity. This causes the oil to leak from the lower part of the roller through the vent hole to stain documents and the like.
Also, when the user detaches the oil application roller from the fixing device and leaves the roller in the state where the rotation axis thereof runs vertically after use, the problem of an oil leak still occurs.
Further, when the fixing device is heated, the internal pressure inside the roller increases to generate water vapor. As a result, the oil held in the oil application roller is extruded though the vent holes of the seal rings, thereby causing an oil escape from the oil application roller. The interior of the fixing device is stained if the oil escape occurs in the fixing device. In addition, the service life of the oil application roller is shortened since the wasteful oil is discharged from the roller and accelerates oil consumption.
The present invention has been made to overcome the above-mentioned problems in the prior art. It is an object of the present invention to provide an oil application roller capable of preventing an oil leak when the roller is left in the state where the rotation axis thereof runs vertically and also capable of preventing an oil escape from the roller in a fixing device. It is another object of the present invention to provide a seal ring for use in the oil application roller and a fixing device using the oil application roller.
In order to achieve the above object, an oil application roller according to the present invention includes: a roller at least including an oil holding portion for holding oil and an oil application surface for applying the oil; a gas release hole provided at respective end portions of the roller in a direction of a rotation axis generatrix of the roller; and a seal ring provided at the respective end portions of the roller to liquid-tightly seal the roller. The oil application roller according to the present invention is characterized in that the seal ring has a vent hole extending from the gas release hole to an outside of the seal ring, and the vent hole has a cross-sectional area of not less than 0.01 mm2 and not more than 1 mm2. In this oil application roller, since the cross-sectional area of the vent hole is not less than 0.01 mm2, expanded air and water vapor can be released to the outside of the roller through the vent hole. On the other hand, since the cross-sectional area of the vent hole is not more than 1 mm2, the oil cannot pass through the vent hole easily. Thus, if the oil application roller is left in the state where the rotation axis thereof runs vertically during use, the oil seldom leaks to the outside of the oil application roller through the vent hole of the seal ring.
When the cross-sectional area of the vent hole is less than 0.01 mm2, the expanded air or water vapor generally cannot be released sufficiently to the outside through the vent hole. On the other hand, when the cross-sectional area of the vent hole is more than 1 mm2, the oil passes through the vent hole easily, thereby causing the oil to leak to the outside through the vent hole of the seal ring when the oil application roller is left in the state where the rotation axis thereof runs vertically during use.
In addition, according to the oil application roller of the present invention, since the cross-sectional area of the vent hole is set to be small, even when the temperature of the oil application roller rises in the fixing device, the oil cannot be extruded easily though the vent holes of the seal rings by the expanded air or water vapor.
In the above-mentioned oil application roller of the present invention, it is preferable that the seal ring has an oil reservoir in a concave shape provided at a side in contact with the roller, and the vent hole is provided between the oil reservoir and an outer peripheral surface of the seal ring. According to this preferable example, when the oil application roller is left in the state where the rotation axis thereof runs vertically during use, the portion of the vent hole that faces the outer peripheral surface of the seal ring is kept horizontal. Thus, if the oil accumulates in the vent hole, an oil leak through the vent hole of the seal ring seldom occurs because the oil is not affected by gravity in the portion.
In addition, even if the oil is extruded from the oil holding portion by the expanded air and/or water vapor generated when the temperature of the oil application roller rises in the fixing device, the oil is seldom extruded through the vent holes as a result of the synergistic effect given by the facts that the oil accumulates in the oil reservoirs provided in the seal rings and that the oil cannot pass through the vent holes having a small cross-sectional area.
In this case, it is preferable that the seal ring further comprises a hole at a portion of the oil reservoir, and the vent hole is provided between the hole and an outer peripheral surface of the seal ring. According to this preferable example, even if the oil escapes from the oil holding portion when the oil application roller is left in the state where the rotation axis thereof runs vertically, the oil seldom leaks to the outside of the oil application roller through the vent hole because it takes a long time until the hole is filled with the oil.
In addition, even if the oil is extruded from the oil holding portion by the expanded air and/or water vapor generated when the temperature of the oil application roller rises in the fixing device, the occurrence of an oil escape can be prevented as a result of the synergistic effect given by the facts that the holes provided in the seal rings cannot fill with the oil easily and that the oil cannot pass through the vent holes having a small cross-sectional area.
In this case, it is further preferable that the distance between the center of the seal ring and the peripheral surface of the hole farthest therefrom is 0.98a or less where xe2x80x9caxe2x80x9d is the distance between the center of the seal ring and the inner peripheral surface of the oil reservoir. According to this preferable example, when the oil is extruded from the oil holding portion by the expanded air and/or water vapor generated when the oil application roller is heated in the state where the oil application roller is held in a horizontal position during use, the extruded oil accumulates in the peripheral faces of the oil reservoirs rather than the holes. As a result, the oil seldom leaks to the outside of the oil application roller through the vent hole.
Further, in the above-mentioned oil application roller of the present invention, it is preferable that the vent hole has an anfractuous shape. According to this preferable example, the oil escaping from the oil holder to accumulate in the seal rings seldom passes through the vent holes. As a result, the occurrence of an oil leak from the oil application roller when the roller is left in the state where the rotation axis thereof runs vertically and the occurrence of an oil escape from the roller during use can be further reduced.
As specifically described above, according to the oil application roller according to the present invention, the occurrence of an oil leak when the roller is left in the state where the rotation axis thereof runs vertically can be reduced. Thus, the concern that the document or the like might be stained with the oil leaking from the roller also can be reduced. In addition, since the occurrence of an oil escape in the fixing device can be reduced, the fixing device can be prevented from being stained by the oil. Furthermore, since no wasteful oil is discharged from the oil application roller, an extended service life of the oil application roller can be realized.
Further, a seal ring according to the present invention, which is provided at an end portion of an oil application roller for holding oil and applying the oil to a surface to be applied with the oil to liquid-tightly seal the oil application roller, is characterized in that it includes a vent hole extending from a surface at a side to be in contact with the oil application roller to an outside of the oil application roller and that at least a portion of the vent hole has a cross-sectional area of not less than 0.01 mm2 and not more than 1 mm2.
In the above-mentioned seal ring according to the present invention, it is preferable that the seal ring further includes an oil reservoir in a concave shape provided at a side to be in contact with the roller and that the above-mentioned vent hole is provided between the oil reservoir and an outer peripheral surface of the seal ring. Further, in this case, it is preferable that the seal ring further includes a hole provided at a portion of the oil reservoir and that the vent hole is provided between the hole and an outer peripheral surface of the seal ring. Still further, in this case, it is preferable that the distance between the center of the seal ring and the peripheral surface of the hole farthest therefrom is 0.98a or less where xe2x80x9caxe2x80x9d is the distance between the center of the seal ring and an inner peripheral surface of the oil reservoir.
In the seal ring according to the present invention, it is preferable that the vent hole has an anfractuous shape.
A fixing device according to the present invention includes a fixing means for fixing toner on a recording material utilizing heat and pressure and an oil application roller for applying release oil to the fixing means. The fixing device is characterized in that an oil application roller according to the present invention is used as the oil application roller.